Method of forming folded-stack packaged device using vertical progression folding tool

ABSTRACT

An embodiment of the present invention includes a pusher and a horizontal puncher. The pusher is located underneath a strip of flexible tape attached to a first unit and a sub-assembly, respectively. The pusher pushes the first unit upward vertically. The horizontal puncher punches the first unit horizontally so that the first unit is folded on top of the sub-assembly.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.10/192,293, filed Jul. 8, 2002 now U.S. Pat. No. 7,017,638. ThisDivisional Application claims the benefit of the U.S. patent applicationSer. No. 10/192,293.

BACKGROUND

1. Field

Embodiments of the invention relate to the field of packaging, and morespecifically, to folded-stack packaging.

2. Background

Chip scale technology offers many advantages in electronics packaging.One emerging packaging technique in chip scale technology is micro ballgrid array (μBGA) packaging. μBGA provides the smallest size, highestperformance, and best reliability of currently available packages.Folded-stack μBGA further improves board density and reliability.

Existing techniques for folded-stack μBGA are typically manual,requiring boat-to-boat handling from singulation process to cureprocess. These techniques have a number of drawbacks. First, the processis slow and cumbersome. The μBGA units are processed through a number ofdiscrete steps: saw singulation, first boat handling, folding andadhere, second boat handling, folding and curing, and then traying.Second, it is expensive because several components (e.g., jigs) areneeded.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 is a diagram illustrating a micro ball grid array (μBGA)packaging layout according one embodiment of the invention.

FIG. 2 is a diagram illustrating a folded-stack μBGA packaged deviceaccording to one embodiment of the invention.

FIG. 3 is a diagram illustrating a tool system according to oneembodiment of the invention.

FIG. 4A is a diagram illustrating a first phase of the folding processaccording to one embodiment of the invention.

FIG. 4B is a diagram illustrating a second phase of the folding processaccording to one embodiment of the invention.

FIG. 4C is a diagram illustrating a third phase of the folding processaccording to one embodiment of the invention.

FIG. 4D is a diagram illustrating a fourth phase of the folding processaccording to one embodiment of the invention.

FIG. 5 is a flowchart illustrating an assembly process for folded-stackpackaged devices according to one embodiment of the invention.

DESCRIPTION

An embodiment of the present invention includes a pusher and ahorizontal puncher. The pusher is located underneath a strip of flexibletape attached to a first unit and a sub-assembly, respectively. Thefirst unit is punched out of the strip. The pusher pushes the first unitupward vertically. The horizontal puncher punches the first unithorizontally so that the first unit is folded on top of the second unit.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown in order not toobscure the understanding of this description.

One embodiment of the invention may be described as a process which isusually depicted as a flowchart, a flow diagram, a structure diagram, ora block diagram. Although a flowchart may describe the operations as asequential process, many of the operations can be performed in parallelor concurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed.A process may correspond to a method, a program, a procedure, etc.

FIG. 1 is a diagram illustrating a micro ball grid array (μBGA)packaging layout 100 according to one embodiment of the invention. Thelayout 100 includes a tape carrier 120, and a flexible tape 130.

The tape carrier 120 is typically a metal frame to carry a number ofpackaged devices affixed on the flexible tape 130. The flexible tape 130is a rectangular tape that can be flexibly folded. The flexible tape 130may be a double-sided polyimide tape (e.g., Kapton or Upilex) having athickness of about 10 μm to 75 μm. The packaged devices are affixed onthe flexible tape 130 in a number of rows and columns. In oneembodiment, there are three rows and N columns. Typically values of Nare 16, 20, 24, 32, etc.

Each column corresponds to a strip of the flexible tape 130 and includesthree units: the first unit 1401, the second unit 1402, and the thirdunit 1403. Each of the units includes a die affixed to a correspondingportion of the flexible tape 130. For example, the first unit 1401, thesecond unit 1402, and the third unit 1403 include a first die, a seconddie, and a third die, respectively, affixed to a first portion 1351, asecond portion 1352, and a third portion 1353, respectively, of thestrip. Each side of the flexible tape 130 may have a metal layer thathas leads and/or interconnections between the die. The die may be anysemiconductor chip or devices such as memory device, flash memory,static random access memory (SRAM), dynamic random access memory (DRAM),logic devices, processing elements, etc. The die are affixed to theflexible tape 130 with die-attaching materials based on silicon orepoxy. The die may also be lead-bonded and encapsulated. The die areattached to the strip by solder balls.

The packaged devices on the flexible tape 130 are packaged and processedaccording to traditional packaging techniques. In one embodiment, thepackaging technique is the μBGA. The packaged devices on each strip orcolumn are folded in a stacking manner to form a folded-stack μBGA.

FIG. 2 is a diagram illustrating a folded-stack μBGA packaged device 200according to one embodiment of the invention.

The folded-stack device 200 includes first, second, and third die 2101,2102, and 2103, respectively, and the flexible tape 130. As discussedabove, the first, second, and third die 2101, 2102, and 2103 areattached to the flexible tape 130 via solder balls 210. The solder balls210 are micro grid array of soldering materials attached to the pads onthe flexible tape 130. The flexible tape 130 is folded in two folds. Inthe first fold, the first die 210, is positioned such that its surfaceis affixed to the surface of the second die 2102 by an adhesive. Theaffixed first and second die 2101 and 2102 form a partially folded unit.In the second fold, the third portion of the flexible tape 130 attachingto the third die 2103 is folded on top of the partially folded unit. Thesurface of the third die 2103 is affixed to the bottom side of the firstportion of the flexible tape 130 by adhesive.

The folded-stack μBGA packaged device 200 as formed is compact andprovides high density and high reliability on a printed circuit board.The process to fold the μBGA packaged device 200 is performed in aprogressive manner in an assembly line that may include severalstations. The folding process is efficiently performed by using a toolassembly for folding, affixing, and curing.

FIG. 3 is a diagram illustrating a tool system 300 according to oneembodiment of the invention. The system 300 includes a strip puncher310, a folding base 320, a first tool assembly 330 and a second toolassembly 340.

The strip puncher 310 punches a strip 125 out of the flexible tape 130.The strip 125 has first, second, and third units 1401, 1402, and 1403.The strip puncher 310 punches vertically from the top down. The punchedstrip 125 is placed on the folding base 320. Adhesive is applied to thesurface of the first and third units 1401 and 1403 so that they areattached when folded together. The application of adhesive may takeplace before or after the vertical punching. Adhesive is dispensed onthe surface by any suitable method.

The folding base 320 provides support for the strip 125. The foldingbase 320 has a first housing 324 and a second housing 326. The first andsecond housings 324 and 326 are located underneath the first and thirdunits 1401 and 1403, respectively, to house first and second pushers 350and 370. Each of the first and second housings 324 and 326 has anopening at the top to allow the corresponding pusher to move upward topush the corresponding unit upward in a substantially verticaldirection.

The first tool assembly 330 includes the first pusher 350 and a firsthorizontal puncher 360. The first pusher 350 and the first horizontalpuncher 360 may be separate or mechanically linked to operate in alockstep fashion. The first tool assembly 330 folds the first unit 1401on top of the second unit 1402. The first pusher 350 is located in thefirst housing 324 underneath the first unit 1401. The first pusher 350includes a first pin 354 and a first spring assembly 356. The first pin350 ejects or moves from a first position to a second position uponbeing activated by an activating mechanism. When the first pin 350 movesupward through the opening of the first housing 324, it pushes the firstunit 1401 upward vertically. The first spring assembly 356 is attachedto the first pin 350 to exert a spring action to the first pin 350 sothat the first pin 350 returns to the first position from the secondposition when the activating mechanism is de-activated or when theactivating force is removed. The first horizontal puncher 360 punchesthe first unit 1401 horizontally when it is pushed upward so that it isfolded on top of the second unit 1402. In addition to delivering thehorizontal punch, the first horizontal puncher 360 also cures theadhesive by dissipating heat at the tip or the distal end. The firsthorizontal puncher 360 is typically made of strong material with highthermal conductivity such as metal. It may be launched by a launcher(not shown) with a spring or spring-like action so that it can beretracted after adhesive curing. The first horizontal puncher 360includes a heating element 362 to heat its tip or distal end. Theheating element 362 may be any suitable heating element such as aresistor coiled around the puncher.

The second tool assembly 340 is essentially the same as the first toolassembly 330. It includes the second pusher 370 and a second horizontalpuncher 380. The second pusher 370 and the second horizontal puncher 380are similar to the first pusher 350 and the first horizontal puncher360, respectively, except that the second horizontal puncher 380 may belocated at a higher level than the first horizontal puncher 360 to matchthe total thickness of the three units stacking on one another. Thiswould help the puncher 360 to deliver a more effective punch to thethird unit 1403 and exert a sufficient force or pressure on the foldedunit. The second tool assembly 340 folds the third unit 1403 on top ofthe partially folded unit formed by the folded first and second units1401 and 1402.

The tool assemblies 330 and 340 perform folding, affixing, and curing inan efficient manner. They can be used in a single station in an assemblyline process to form folded stack packaged devices. Although the abovedescription is for a three-unit packaged device, the technique can beextended for more than three units. For example, a four-unit packageddevice may need three pushers and two horizontal punchers. A firstpusher folds the first unit on top of the second unit to form asub-assembly or a first partially folded unit using a first horizontalpuncher. A second pusher folds the fourth unit on top of the third unitto form a second partially folded unit using a second horizontalpuncher. A third pusher folds the second partially folded unit on top ofthe first partially folded unit using the second horizontal puncher. Fora three-unit folded stack packaged device, the process may include fourphases.

FIG. 4A is a diagram illustrating a first phase 410 of the foldingprocess according to one embodiment of the invention.

In the first phase 410, an activating force from an activation mechanismis applied to the first and second pins 354 and 356 so that they movefrom a first position to a second position. As the pins 354 and 374 moveto the second position through the opening, the first and third units1401 and 1403 are pushed upward vertically, forming an inclination angleor slope with respect to the surface of the folding base 320. To haveeffective punching, the inclination angle may range from 30° to 70°.When the pins 354 and 374 reach the second position, the first and thirdunits 1401 and 1403 are pushed to form a slope sufficiently steep toallow the first and second punchers 360 and 380 to make proper impactwhen punching. In addition, as the pins 354 and 374 move to the secondposition under the activation force, the corresponding spring assemblies356 and 376 are compressed.

The two horizontal punchers 360 and 380 are prepared to launch thepunch. The heating elements 362 and 382 are activated to heat up the tipor the distal end of the corresponding punchers 360 and 380. This can beaccomplished by applying a voltage across the heating elements 362 and382.

FIG. 4B is a diagram illustrating a second phase 420 of the foldingprocess according to one embodiment of the invention.

In the second phase 420, the first horizontal puncher 360 is activatedto slide or move toward the first unit 1401 in a substantiallyhorizontal direction. The first horizontal puncher 360 impacts the firstunit 1401 and cause the first unit 1401 to fold on top of the secondunit 1402 to form a sub-assembly or a partially folded unit 422. Thefirst horizontal puncher 360 continues to slide horizontally on top ofthe folded first unit on the side of the strip of tape. It is stoppedwhen it reached a predetermined location, usually when it sufficientlycovers the surface of the folded first unit. Since the first horizontalpuncher 360 is at a horizontal level that is approximately equal to thethickness of the first and second units 1401 and 1402 when they arefolded together, it fits on top of the first unit 1401. The firsthorizontal puncher 360 may be firmly guided so that it can exert asuitable force on the folded first unit 1401 to affix it on top of thesecond unit 1402 via the adhesive. The first horizontal puncher 360stays on top of the partially folded unit 422 so that its heated tip ordistal end cures the adhesive.

FIG. 4C is a diagram illustrating a third phase 430 of the foldingprocess according to one embodiment of the invention.

In the third phase 430, the first horizontal puncher 360 finishes curingthe adhesive and the partially folded unit 422. It is then retractedhorizontally to its original position. The second horizontal puncher 380is then activated to impact the third unit 1403 horizontally to fold thethird unit 1403 on top of the partially folded unit 422 to form a foldedstack packed device 432. The second horizontal puncher 360 continues toslide horizontally on top of the partially folded unit 422 on the sideof the strip of tape. Since the second horizontal puncher 380 is at ahorizontal level that is approximately equal to the thickness of thethird unit 1403 and the partially folded unit 422 when they are foldedtogether, it fits on top of the third unit 1403 and exerts a force onthe third unit 1403 to affix it to the partially folded unit 422 via theadhesive. The second horizontal puncher 380 stays on top of thepartially folded unit 422 so that its heated tip or distal end cures theadhesive.

FIG. 4D is a diagram illustrating a fourth phase 440 of the foldingprocess according to one embodiment of the invention.

In the fourth phase 440, the second horizontal puncher 380 finishescuring the adhesive and is retracted or withdrawn to its originalposition. A pick and place tool 445 picks up the folded stack packageddevice 432 and places it to an off-load transport unit or a tray. Theactivation force on the pins 354 and 374 is removed so that the springassemblies 356 and 376 exert a spring force on the pins 354 and 374 topush them back to the first position. The folding process is thuscompleted.

FIG. 5 is a flowchart illustrating an assembly process 500 forfolded-stack packaged devices according to one embodiment of theinvention.

Upon START, the process 500 punches out a strip of flexible tape withthree units from the array of strips (Block 510). The first and thirdunits are on the edges of the strip and the second unit is in the middleof the strip. Next, the process 500 applies adhesive on surface of thefirst and third units (Block 515). Then, the process 500 pushes thefirst and third units upward by pushers located underneath the strip(Block 520). This is accomplished by applying an activation force on thetwo pins of the pushers. The pins move from a first position to a secondposition.

Next, the process 500 punches the first unit horizontally by the firsthorizontal punch so that the first unit is folded on top of the secondunit to form a partially folded unit (Block 525). Then, the process 500cures the adhesive using the heated distal end of the first horizontalpunch (Block 530). Next, the process 500 withdraws the first horizontalpunch (Block 535).

Then, the process 500 punches the third unit horizontally by the secondhorizontal puncher so that the third unit is folded on top of thepartially folded unit (Block 540). Next, the process 500 cures theadhesive on the third unit by the heated distal end of the secondhorizontal puncher (Block 545). Then, the process 500 withdraws thesecond horizontal puncher to its original position (Block 550).

Next, the process 500 removes the folded stack packaged device by a pickand place tool and retracts the pushers to their first position (Block555). Then, the process 500 is terminated.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

1. A method comprising: pushing a first unit upward vertically by apusher located underneath a strip of flexible tape attached to the firstunit and a sub-assembly, the first unit having a first die; and punchingthe first unit horizontally by a horizontal puncher so that the firstunit is folded on top of the sub-assembly; wherein pushing comprises:activating a pin to move the pin from a first position to a secondposition, the pin pushing the first unit upward vertically; andspringing the pin to return to the first position from the secondposition by a spring assembly.
 2. The method of claim 1 wherein pushingthe first unit comprises pushing the first die attached to a firstportion of the strip.
 3. The method of claim 2 further comprisesattaching a second die to a second portion of the strip to form thesub-assembly.
 4. The method of claim 2 further comprises forming thesub-assembly by a partially folded unit.
 5. The method of claim 4wherein forming the sub-assembly comprises: attaching a second unit to asecond portion of the strip; and folding a third unit on top of thesecond unit, the third unit being attached to a third portion of thestrip, the third unit being attached to the second unit via adhesive. 6.The method of claim 5 further comprising attaching a second die in thesecond unit to one of the second and third portions.
 7. The method ofclaim 1 wherein one of the first unit and the sub-assembly includes amicro ball grid array (μBGA) packaged device.
 8. A method comprising:pushing a first unit upward vertically by a pusher located underneath astrip of flexible tape attached to the first unit and a sub-assembly,the first unit having a first die; and punching the first unithorizontally by a horizontal puncher so that the first unit is folded ontop of the sub-assembly; and dispensing one of the first unit and thesub-assembly with adhesive; wherein punching comprises heating a distalend of the horizontal puncher to cure the adhesive when the first unitis folded on top the sub-assembly.
 9. The method of claim 8 whereinpushing the first unit comprises pushing the first die attached to afirst portion of the strip.
 10. The method of claim 9 further comprisesattaching a second die to a second portion of the strip to form thesub-assembly.
 11. The method of claim 9 further comprises forming thesub-assembly by a partially folded unit.
 12. The method of claim 11wherein forming the sub-assembly comprises: attaching a second unit to asecond portion of the strip; and folding a third unit on top of thesecond unit, the third unit being attached to a third portion of thestrip, the third unit being attached to the second unit via adhesive.13. The method of claim 12 further comprising attaching a second die inthe second unit to one of the second and third portions.
 14. The methodof claim 8 wherein one of the first unit and the sub-assembly includes amicro ball grid array (μBGA) packaged device.